Foseco Ferrous Foundryman''''s Handbook Part 13 pdf

290 Foseco Ferrous Foundryman’s Handbook differences between conventional systems and direct pour practice. The examples shown in Fig. 18.13 illustrate the benefits obtained by the application of a KALPUR ST unit to a valve casting. Productivity improvements The KALPUR ST unit can be applied to a range of casting types. Impellers, for example, are usually cast with heavy running systems up into the centre of the casting body. A KALPUR ST unit can be applied as a central feeder, (see Fig. 18.14) and the metal poured directly into the casting. More castings can thereby be obtained from a ladle of metal. The promotion of excellent directional solidification has also resulted in the reduction in size or total removal of feeders on the perimeter of the casting (Fig. 18.15). Selecting the proper size and positioning the KALPUR unit There are two basic designs of unit, one for side feeder application and one for top feeder application, Fig. 18.16a, b. KALPUR ST units are supplied in a range of sizes (Fig. 18.11) having capacity from around 30 kg to over 250 kg of carbon or low alloy steel and more for high alloy steel (Table 18.4). Metal temperature, ladle practice (bottom versus lip pour), melting practice (cleanliness), metal deoxidation, and steel composition all determine the amount of metal that can be poured before filter blockage that would prevent proper pouring or adequate feeding after the mould is filled. Factors resulting in low capacities and flow rates: Figure 18.12 The KALPUR ST unit is placed as close to the casting cavity as possible to preserve laminar flow from the filter. Filtration and the running and gating of steel castings 291 Figure 18.13 (a) Temperature distribution within a valve casting immediately after filling through a conventional gating system. Large areas are much colder than the last metal poured. (b) Temperature distribution within a valve casting immediately after filling through a KALPUR unit shows higher overall temperature, illustrating reduced heat loss when direct pour units are used. (This figure is reproduced in colour plate section.) (a) (b) Temperature Distribution in the Casting at the End of Filling … Conventional Gating Temperature Distribution in the Casting at the End of Filling … Direct Pour 292 Foseco Ferrous Foundryman’s Handbook Figure 18.14 KALPUR unit used as a central feeder. Conventional method New KALPUR ST direct pour system Figure 18.15 The KALPUR ST direct pour system eliminates the conventional running system and reduces feeder requirements. Filtration and the running and gating of steel castings 293 Figure 18.16 KALPUR ST unit: (a) for side feeder application; (b) for top feeder application. (a) (b) Table 18.4 Capacity and flow rates of KALPUR ST units Capacity range (kg) Nominal flow rate (kg/s) (at 300 mm metallostatic pressure) KALPUR High level of Low level of Carbon Stainless size deoxidation deoxidation steel steel products products KALPUR 50 30 90 2.0 3.0 KALPUR 75 65 200 4.4 6.6 KALPUR 100 120 355 7.8 11.7 KALPUR 125 185 550 12.2 18.4 KALPUR 150 265 795 17.7 26.5 Deoxidation with Zr, Ti Molten metal containing large quantities of inclusion material Low metal pouring temperatures Low metallostatic pressure on filter. A minimum pouring temperature of 1580°C for carbon steel and 1520°C for stainless steel is recommended to ensure priming. 294 Foseco Ferrous Foundryman’s Handbook The KALPUR ST system acts as an insulating feeder sleeve of similar size. The presence of a filter in a unit does not affect the feed efficiency. An efficient anti-piping compound should be applied to the KALPUR ST immediately after pouring is finished. Recommended materials are: KALPUR ST 50 and 75 FERRUX 16 KALPUR ST 100, 125, 150 FERRUX 707F The KALPUR ST system can incorporate a neck-down feature for reduced fettling and the possibility of knock-off. To select the proper KALPUR ST unit for a given application, two criteria must be met: feeding capacity and filtration performance. First, one must determine which unit sleeve is large enough to satisfy the feeding requirement. Next, the filter in that unit must be evaluated for filtration capacity and flow rate. If the filtration capacity or flow rate is inadequate for the mould weight, cleanliness of the metal, or maximum pour time, a bigger KALPUR unit having a larger filter should be selected. The KALPUR unit is rammed into position. It should be placed as close to the casting as possible and ideally should be located no more than 150 mm above the impact area (Fig. 18.12). Cost savings through the use of STELEX and KALPUR An analysis of steel casting cleaning costs has been undertaken by the Institut fur Giessereitechnik, Dusseldorf covering a number of steel foundries representing 10% of German steel casting production. The work showed that the cleaning costs associated with a casting can amount to 40% of its total manufacturing cost. Cleaning costs were further broken down as follows: Reworking of casting defects 37% (inclusions, penetration, shrinkage) Removal of feeding and gating systems 27% Removal of rough surfaces 20% (fins, flash and burn-on) Others 16% Of these costs 52% were considered as avoidable 31% were considered as possibly avoidable 17% were defined as unavoidable Filtration and the running and gating of steel castings 295 The use of STELEX ZR filters and KALPUR ST units enables major reductions to be made in the avoidable cleaning costs through simplification of gating and feeding systems and the removal of inclusions. Chapter 19 Feeding of castings Introduction During the cooling and solidification of most metals and alloys, there is a reduction in the metal volume known as shrinkage. Unless measures are taken which recognise this phenomenon, the solidified casting will exhibit gross shrinkage porosity which can make it unsuitable for the purpose for which it was designed. To some extent, grey and ductile cast irons are exceptions, because the graphite formed on solidification expands and can compensate for the metal shrinkage. However, even with these alloys, measures may need to be taken to avoid shrinkage porosity. To avoid shrinkage porosity, it is necessary to ensure that there is a sufficient supply of additional molten metal, available as the casting is solidifying, to fill the cavities that would otherwise form. This is known as ‘feeding the casting’ and the reservoir that supplies the feed metal is known as a ‘feeder’, ‘feeder head’ or a ‘riser’. The feeder must be designed so that the feed metal is liquid at the time that it is needed, which means that the feeder must freeze later than the casting itself. The feeder must also contain sufficient volume of metal, liquid at the time it is required, to satisfy the shrinkage demands of the casting. Finally, since liquid metal from the feeder cannot reach for an indefinite distance into the casting, it follows that one feeder may only be capable of feeding part of the whole casting. The feeding distance must therefore be calculated to determine the number of feeders required to feed any given casting. The application of the theory of heat transfer and solidification allows the calculation of minimum feeder dimensions for castings which ensures sound castings and maximum metal utilisation. Natural feeders Feeders moulded in the same material that forms the mould for the casting, usually sand, are known as natural feeders. As soon as the mould and feeder have been filled with molten metal, heat is lost through the feeder top and side surfaces and solidification of the feeder commences. A correctly dimensioned feeder in a sand mould has a characteristic solidification pattern: that for steel is shown in Fig. 19.1 the shrinkage cavity is in the form of a cone, the volume of which represents only about 14% of the original volume Feeding of castings 297 of the feeder, and some of this volume has been used to feed the feeder itself, so that in practice only about 10% of the original feeder volume is available to feed the casting. The remainder has to be removed from the casting as residual feeder metal and can only be used for re-melting. Figure 19.1 Solidification pattern of a feeder for a steel casting (schematic). Aided feeders – feeding systems If by the use of ‘feeding systems’ the rate of heat loss from the feeder can be slowed down relative to the casting, then the solidification of the feeder will be delayed and the volume of feed metal available will be increased. The time by which solidification is delayed is a measure of the efficiency of the feeding aid. The shape of the characteristic, conical, feeder shrinkage cavity will also change and in the ideal case, where all the heat from the feeder is lost only to the casting, a flat feeder solidification pattern will be obtained (Fig. 19.2). As much as 76% of an aided feeder is available for feeding the casting compared with only 10% for a natural sand feeder. This increased efficiency means greatly reduced feeder dimensions with the following advantages for the foundry: A greater number of castings can be produced from the given weight of liquid metal Smaller moulds can be used, saving on moulding sand costs A reduction in the time needed to remove the feeder from the casting is possible More castings can be mounted on the pattern plate and thus into the mould Less metal is melted to produce a given volume of castings Maximum casting weight potential is increased Smaller feeders mean less fettling time and cost. 298 Foseco Ferrous Foundryman’s Handbook Feeding systems Side wall feeding aids are used to line the walls of the feeder cavity and so reduce the heat loss into the moulding material. For optimum feeding performance, it is also necessary to use top surface feeding aids. These are normally supplied in powder form and are referred to as anti-piping or hot- topping compounds. Figure 19.3 illustrates how the use of side wall and top surface feeding aids extends the solidification times. Now, however, suitable insulating discs (lids) are increasingly being used in place of hot-topping compounds for environmental reasons. For mass production castings 90% of feeders are closed or ‘blind’. Figure 19.2 Ideal feeder solidification pattern where all the heat from the feeder has been lost to the casting (schematic). Solidification time Sand wall open top KALMINEX sleeve open top 29.2 minutes 39.8 minutes Sand wall FERRUX cover KALMINEX sleeve FERRUX cover 44.9 minutes 73.1 minutes Figure 19.3 Extension of solidification times with side wall and top surface feeding products for a steel cylinder 250 mm dia. and 200 mm high. Feeding of castings 299 Calculating the number of feeders – feeding distance A compact casting can usually be fed by a single feeder. In many castings of complex design the shape is easily divided into obvious natural zones for feeding, each centred on a heavy casting section separated from the remainder of the casting by more restricted members. Each individual casting section can then be fed by a separately calculated feeder and the casting shape becomes the main factor which determines the number of feeders required. In the case of many extended castings however, for example the rim of a gear wheel blank, the feeding range is the factor which limits the function of each feeder and the distance that a feeder can feed, the ‘feeding distance’, must be calculated. The feeding distance from the outer edge of a feeder into a casting section consists of two components: The end effect (E), produced by the rapid cooling caused by the presence of edges and corners. An effect (A), produced because the proximity of the feeder retards freezing of the adjacent part of the casting (Fig. 19.4). Where a casting requires more than one feeder the distance between feeders is measured from the edge of the feeder, not from its centre; and when the feeder is surrounded by a feeder sleeve the distance between feeders is measured from the outside diameter of the sleeve. The effective distance between feeders can be increased by locating a chill against the casting mid-way between the two feeders (X1) and the natural end effect can be increased by locating a chill against the natural end (X). Chills should be of square or rectangular section with the thickness approximately half the thickness of the section being chilled. There are therefore four possible situations: Sections with natural end effect only (A+E) Sections with natural end effect plus end chill (A+E+X) Sections with no end effect (A) Sections with no end effect plus chill (A+X 1 ) Figure 19.4 shows the basis for calculating feeding distance in steel castings and all other ferrous alloys which freeze white, e.g. malleable and high alloy irons. Ductile and grey iron castings Alloy composition, casting section, mould materials and mould hardness all play a part in determining the actual feeding distance. The following tables are guidelines for green sand moulds having mould hardness 90° B scale, variations from these conditions will result in other feeding distances. [...]... there is a description of the various aids such as tables, nomograms, and computer programs developed by Foseco to make the determination of feeder dimensions much easier The modulus concept Although this concept has some shortcomings it is, with the exception of 302 Foseco Ferrous Foundryman’s Handbook computer programs, the most widely used acceptable and accurate method for calculating feeder dimensions... feeder diameter below that necessary to meet modulus requirements The following data is necessary 306 Foseco Ferrous Foundryman’s Handbook (a) The proportion of feed metal available from the feeder which meets modulus requirements (C%) Safe values although not necessarily the most efficient are: 33–50% if a Foseco sleeve is being used 14–16% if it is a live natural feeder (i.e one through which metal has... percentage of solidification time Effective feeder modulus is determined by: MF = Mc × 1.2√ST/100 (c) Provisional determination of the feeder from feeder sleeve tables published by Foseco companies 308 Foseco Ferrous Foundryman’s Handbook a (cm) 2 5 10 20 50 100 100 ,0 20 18 16 4 1 50 b (cm) 50 12 0 10 0 9 .0 8 0 7 .0 6 0 5 5 4 .0 4 5 3 .0 3 5 2 0 2 .8 1 6 1 .4 1 2 1 0 1 9 0 .8 0 7 0 .6 0 5 0 20 10 5 100... (a) The proportion of feed metal available from the feeder which meets modulus requirements (C%) Safe values although not necessarily the most effective are: 33–50% if a Foseco sleeve is being used; 310 Foseco Ferrous Foundryman’s Handbook 14–16% if it is a live natural feeder (i.e one through which metal has to flow before it reaches the casting cavity in the mould); 10% for other natural feeders... cores KALMIN S feeder sleeves By using a high proportion of light refractory raw materials, a density of 0.45 g/cm3 is achieved, ensuring highly insulating properties KALMIN S 312 Foseco Ferrous Foundryman’s Handbook sleeves are particularly suitable for aluminium, copper-base and iron alloy sand castings since the raw materials used are neutral to both the casting alloys and to the moulding sand KALMIN... 9.0 Non -ferrous castings Table 19.3 gives a feeding distance factor for some of the non -ferrous alloys; this factor is used in the calculation of an approximate feeding distance Feeding of castings 301 Table 19.2 Feeding distance factor (FD) for grey iron castings Carbon equivalent (%) Feeding distance factor (FD) 3.0 3.4 3.9 4.3 6.8 7.7 8.8 10.0 Table 19.3 Feeding distance factor for non -ferrous. ..300 Foseco Ferrous Foundryman’s Handbook 2.5t 2t 2t 2t 2t 2.5t t A 5t A 5t E 5t 5t t X1 + A A+E+X (a) 1.5t 1.5t 6 t A A+E 6 t+t 6 t+t t X1 + A A+E+X (b) Figure 19.4 Feeding distance in steel castings (a) Plate (width: thickness... Endless cylinder (ends terminated by another part of casting) D 4 Note: Because radial heat flow is faster than that from D a flat surface, calculated moduli for endless cylinders may be reduced Diameter = D by multiplying by 0.85 (f) Endless plate (terminated on all sides by another part of casting) T T 2 Thickness = T W (g) Endless bar (ends terminated by another part of casting) T Thickness = T Width... equation (Fig 19.5g) or the diagram in Fig 19.6 Foseco feeding systems Introduction Foseco provides complete feeding systems for foundries, comprising Sleeves – insulating, exothermic and exothermic-insulating for all metals Feeding of castings 311 Breaker cores – to aid removal of the feeder from the casting Sleeve/filter units Application technology – to suit the particular moulds and moulding machine used... D2 Wall thickness = T T T (i) Annulus Figure 19.5 D1 D2 H D1 – D 2 =T 4 2 (D 1 – D 2 ) 2(D 1 – D 2 ) + H OD = D1 Dia core = D2 Modulus formulae for some common shapes = TH 2(T + H ) 304 Foseco Ferrous Foundryman’s Handbook k can therefore be reduced to its two constituent components so that k = cf 2 where c is a constant depending on the properties of the metal being cast; f 2 is a constant depending . result in other feeding distances. 300 Foseco Ferrous Foundryman’s Handbook Non -ferrous castings Table 19.3 gives a feeding distance factor for some of the non -ferrous alloys; this factor is used. 290 Foseco Ferrous Foundryman’s Handbook differences between conventional systems and direct pour practice. The examples shown in Fig. 18 .13 illustrate the benefits obtained. Provisional determination of the feeder from feeder sleeve tables published by Foseco companies. 308 Foseco Ferrous Foundryman’s Handbook 3. Calculate the feed volume requirement Feeders, whose dimensions